Somayeh Lotfi

Recycling of End of Life Concrete Fines (0–4 mm) from Waste to Valuable Resources

End of Life (EOL) concrete fines, that is often 0–4 m, is one of the massive by-products of concrete recycling. Using this fraction into new concrete is detrimental, due to its high water absorption and mixed contaminants. Although the construction sector is to some extent familiar with the utilization of the coarse fraction of crushed concrete, at present there is no high-quality application for crushed concrete fines. Here we present an effective recycling process on lab scale to separate the cementitious powder from the sandy part in the crushed concrete fines and deliver attractive products with the minimum amount of contaminants. For this study, a lab scale Heating-Air classification System (HAS) was designed and constructed. A combination of heat and air classification, resulted in a proper separation of finer fraction (0–0.250 mm), from coarser fractions. Heating of the materials was followed by ball milling to enhance the liberation of the cementitious fraction. Experiments were carried out at different heating temperatures and milling durations. Experimental results show that by heating the materials to 500 °C for 30 s, the required time of ball milling is diminished by a factor of three and the quality of the recycling products satisfies the market demand. In addition, the removal of contaminants is complete at 500 °C. The amount of CaO in the recovered finer fraction from the recycling process is comparable with the amount of CaO in low-quality limestone. By using this fraction in the cement kiln as the replacement of limestone, the release of the chemically bound CO2 could be reduced by a factor of three. This proof of concept constitutes the starting point for the new HAS technology proposed in the Horizon 2020 VEEP project.